Surface Winds and Enthalpy Fluxes During Tropical Cyclone Formation From
Easterly Waves: A CYGNSS view
Abstract
We examined the Cyclone Global Navigation Satellite System (CYGNSS)
retrievals of surface winds and enthalpy fluxes in African easterly
waves that led to the formation of 31 Atlantic tropical cyclones from
2018–2021. Lag composites show a cyclonic proto-vortex as early as 3
days prior to tropical cyclogenesis. The distribution of enthalpy fluxes
within the proto-vortex does not vary substantially prior to
cyclogenesis, but subsequently, there is an increase in the upper
extreme values. A negative radial gradient of enthalpy fluxes becomes
apparent as early as 2 days before cyclogenesis. These results—based
on a novel data blending satellite retrievals and global
reanalysis—are consistent with recent studies that have found that
tropical cyclone spin-up is associated with a shift of peak convection
towards the vortex-core and a radially inward increase of enthalpy
fluxes. They provide additional evidence for the importance of surface
enthalpy fluxes and their radial structure for tropical cyclogenesis.